Static dissipation treatments for optical package windows

ABSTRACT

An optically transparent conductive material is disposed directly or indirectly on an inside surface of a cover material for static dissipation in an optical switching device. The optically transparent conductive material forms an electrically continuous film. The optically transparent conductive material can also be used for anti-reflection. An additional coating may be disposed directly or indirectly on an outside surface of the cover material.

PRIORITY

This application is a divisional of, and therefore claims priority from,co-pending U.S. patent application Ser. No. 10/101,016 entitled STATICDISSIPATION TREATMENTS FOR OPTICAL PACKAGE WINDOWS, which was filed onMar. 19, 2002 in the names of John R. Martin, Maurice Karpman, andLawrence E. Felton, and which is hereby incorporated herein by referencein its entirety.

FIELD OF THE INVENTION

The present invention relates generally to optical switching, and moreparticularly to static dissipation treatments for optical packagewindows.

BACKGROUND OF THE INVENTION

Micro-machined optical switching devices for use in optical switchingapplications, often referred to as Micro Electromechanical Systems(MEMS) or Micro Opto Electromechanical Systems (MOEMS) and referred tohereinafter as a MOEMS, typically contain optical mirrors that arecontrollable electronically. The optical mirrors are typicallymicro-machined from a silicon wafer and coated with various materials toproduce a reflective mirror surface. The mirror structure is typicallybonded onto a substrate, specifically within a pre-formed cavity in thesubstrate. An optical transparent window (referred to hereinafter forconvenience as a “cover”) is typically bonded onto the substrate acrossthe cavity. The cover is typically a glass material, such asborosilicate glass or fused silica. The cover allows light to pass toand from the optical mirrors and protects the extremely fragile mirrors.

The substrate or silicon wafer typically includes electrode pads thatare used to control the position of the optical mirrors, and alsoincludes various electrical contacts. The optical mirrors must bepositioned a precise distance above the electrode pads because they arecontrolled through electrostatic forces, and the voltage required toposition a mirror depends on, among other things, the distance of themirror from the electrode pads. Variations in the distance between themirrors and the electrode pads make it difficult to control the positionof the mirrors.

Reflections produced by the MOEMS cover surfaces can impact the opticalswitching performance of the MOEMS. Therefore, an antireflective (AR)coating is typically placed on one or both MOEMS cover surfaces toreduce reflections.

Electrostatic charge buildup on the MOEMS cover surfaces can degrade thepositional accuracy and stability of the MOEMS mirrors. One solution isto make the cover (or its surfaces) conductive so the cover can begrounded, specifically by applying an electrically conductive film tothe cover surfaces. Unfortunately, most conductive materials are opaque.Certain conductive inorganic oxides, often based on ITO (indium-tinoxide), have been used for similar applications in which electricallyconductive surfaces are required on optically transparent windows (e.g.,solar cells, photodetectors, and cathode ray tube (CRT) surfaces, toname but a few), although such conductive inorganic oxides typicallyprovide insufficient transparency in the near infrared region at whichthe MOEMS typically operate, particularly at wavelengths around 1.3microns and 1.5 microns (1.3μ and 1.5μ).

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, an optically transparentconductive material is used for static dissipation of a cover materialfor an optical switching device. An optically transparent conductivematerial is disposed directly or indirectly on an inside surface of thecover material. Optionally, an optically transparent conductive materialmay additionally be disposed directly or indirectly on an outsidesurface of the cover material. The optically transparent conductivematerial(s) can also be used for anti-reflection. The optical switchingdevice may include integrated electronic circuitry.

In certain embodiments of the invention, certain ionomers are used toform an electrically conductive film for static dissipation of a covermaterial for an optical switching device. Exemplary ionomers for staticdissipation of a cover material for an optical switching device includeperfluorosulfonic acid copolymerized with tetrafluoroethylene andmethacrylic acid copolymerized with ethylene. An ionizing medium may beused to ionize the ionomer. The ionizing medium may be integrated withthe optically transparent conductive material or may form a separatelayer of material. Exemplary ionizing media include certain highmolecular weight alcohols, such as such as glycerol,1,2,3,4-butanetetrol, polyvinyl alcohol, or polyethylene oxide.

In certain other embodiments of the invention, electrically conductiveparticles are added to an optically transparent medium such as Teflon AFto form an electrically conductive film for static dissipation of acover material for an optical switching device. Exemplary electricallyconductive particles include single wall carbon nanotubes (SWNT)sufficiently dispersed throughout the Teflon AF so as to provideelectrical continuity across the film while maintaining sufficientoptical transparency.

Certain other embodiments of the invention utilize surface forces aloneto hold dispersed nanoscale particles such as SWNT on the cover materialsurface, even if they are not held in a medium film.

In alternative embodiments, the cover material may include a metallizedfilm for bonding to a metal frame, and the optically transparentconductive coating may contact at least a portion of the metallizedfilm.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 shows an exemplary MOEMS in accordance with an embodiment of thepresent invention; and

FIG. 2 shows a cross-sectional view of an exemplary MOEMS cover inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows an exemplary MOEMS 100 in accordance with an embodiment ofthe present invention. Among other things, the MOEMS 100 includes amirror structure 106 that is bonded to a substrate 102 using a bondingmaterial 104. The mirror structure 106 is bonded to the substrate 102within a pre-formed cavity 110 in the substrate 102. A cover 108 isbonded to the substrate 102 across the cavity 110, thereby covering themirror structure 106. The mirror structure 106 typically includesoptical mirrors that are controllable electronically. The mirrorstructure 106 is typically formed from a silicon wafer. The mirrors aretypically micro-machined from the silicon wafer and coated with variousmaterials to produce a reflective mirror surface. The cover 108 istypically a glass material, such as borosilicate glass or fused silica.The cover 108 allows light to pass to and from the optical mirrors andprotects the extremely fragile mirrors of the mirror structure 106. TheMOEMS 100 optionally includes integrated electronic circuitry formonitoring and controlling the mirror positions.

In an embodiment of the present invention, any of a variety of opticallytransparent conductive materials is used to make the MOEMS coverelectrically conductive so the MOEMS cover can be grounded. Theoptically transparent conductive material is typically included as oneor more thin film layers of the antireflective (AR) coating deposited onthe MOEMS cover. The optically transparent conductive material can bedeposited using any of a variety of techniques, and the presentinvention is in no way limited to any particular technique fordepositing the optically transparent conductive material. Certainoptically transparent conductive materials have antireflective (AR)properties, and can be used for static dissipation and/orantireflection.

FIG. 2 shows a cross-sectional view of an exemplary MOEMS cover 108.Among other things, the MOEMS cover 108 includes a cover material 220.The cover material 220 is typically a glass material, such asborosilicate glass or fused silica. In order to reduce optical loss,both surfaces of the cover material 220 are typically coated with an ARcoating (film stack) 210 and 230, respectively. Each AR coating (filmstack) 210, 230 includes at least one thin film layer. At least one ofthe AR coatings (film stacks) 210 and 230 includes an opticallytransparent conductive material for static dissipation of the MOEMScover 108.

A candidate for an optically transparent conductive material should havelittle (if any) absorption in the near infrared region at which theMOEMS typically operates (particularly at wavelengths around 1.3μ and1.5μ), should have process characteristics that allow it to be appliedas a controlled-thickness thin film with properties that can beintegrated into the stack of materials deposited onto the MOEMS cover,and should be optically and electrically stable over the product life.The overall design of the stack of materials deposited on the MOEMScover should take into consideration the characteristics of theoptically transparent conductive material, such as its refractive indexand thickness.

The cover may include a metallized film around its periphery throughwhich an electrical connection can be made to the cover, for example,for electrically grounding the cover. The optically transparentconductive film preferably overlaps or is otherwise in electricalcontact with the metallized film so that static electricity from thecover can flow to the metallized film.

The cover can be bonded to the MOEMS package using any of a variety ofbonding techniques. For example, the cover can be bonded to the MOEMSpackage by soldering the metallized film to the MOEMS package.Alternatively, a metal frame may be soldered to the metallized film, andthe metal frame may be seam-sealed to the MOEMS package. Excess filmmaterial can be removed from the solder joint region, for example, usinga plasma etching technique. A metal stencil shadow mask can be used toallow the excess film material to be removed from the solder areas whileprotecting it in the optical area of the MOEMS cover.

The process by which the frame is attached to the cover is typicallydone under high temperatures. Selection of an optically transparentconductive material should take into consideration this and otherexposure temperatures.

Ionomer Films

One class of optically transparent conductive materials is known as“ionomers.” An ionomer is a conductive organic polymer whoseconductivity is based upon high ion mobility. Polymers that containionic groups are known as polyelectrolytes. Ionomers are specialpolyelectrolytes that contain both ionic and nonionic groups. They areusually copolymers, in which ionic and nonionic monomers are linedtogether to form a long chain. Only a small percentage of the ionicmonomer (seldom more than 20 percent) is sufficient to achieve theproperties normally sought in ionomers. A molecular view would typicallyshow long chains of nonpolar segments linked with polar ionic groups inthe same molecule. The polar groups of adjacent molecules are attractedto each other, so they cluster together, producing an effect thatresembles chemical crosslinks. However, these clusters can be reversiblybroken and re-formed, normally by heat during thermoplastic processing,but also by interactions with polar liquids.

It should be noted that ionomers are not electrically conductive untilthey are ionized. Thus the ionomer is typically used in conjunction withan ionizing medium.

The nature of the ionizable group in ionomers affects their electricalproperties. For example, sulfonic acid is more ionizable than carboxylicacid. Therefore, all else being equal, sulfonic acid based ionomersgenerally produce films with higher conductivity than carboxylic acidbased ionomers.

Copolymer ratio is also important.

One candidate ionomer for MOEMS static dissipation films isperfluorosulfonic acid copolymerized with tetrafluoroethylene, which isreferred to hereinafter as PAT. PAT is an optically clear sulfonic acidbased ionomer that is commercially available under the name NAFION™. PATis commonly used as a semi-permeable or ion-selective membrane forremoving ions in water purification applications. PAT is notelectrically conductive until it is ionized by an ionizing medium. PATis commercially available as alcohol/water solutions.

Various aspects of the present invention are demonstrated by examplewith reference to an exemplary MOEMS using PAT ionomer films for staticdissipation.

PAT has certain properties that make it a good candidate for MOEMSstatic dissipation films. At low sulfonic acid levels, PAT films tend toswell and become conductive in water. At higher levels, thesefluoropolymers actually dissolve in alcohols. This allows PAT films tobe readily formed by spin coating. Like other fluoropolymers, PAT isoptically and thermally stable.

Both water and alcohol make PAT conductive. However, water and alcoholare not ideal for anti-static coatings on MOEMS covers. Rather, a lessvolatile ionizing medium is typically used to ionize the PAT film. Thatbeing said, it is virtually impossible to completely remove water from aPAT film because PAT is generally hygroscopic, particulary the gradesthat are sold as solutions (solution grades probably have a higherproportion of the perfluorosulfonic acid monomer in order to obtain astable solution). At equilibrium, water (or an alcohol) in the sealedpackage would be “partitioned” between the PAT and the gas in thecavity. To the extent that they remain in the PAT, these volatilespecies contribute to ionic conductivity, and perhaps even meet asignificant part of the total ionic conductivity requirement. The PATand low volatility ionizing medium can be deposited onto the MOEMS coverusing any of a variety of techniques, and the present invention is in noway limited to any particular technique for depositing the PAT andnon-volatile ionizing medium onto the MOEMS cover. The MOEMS covertypically has a metal frame that is later seam-sealed to the MOEMSpackage. This frame is typically soldered to a metallized film that isdeposited around the periphery of the cover. To make electricalconnections, the PAT film should overlap onto the metallized film.Excess PAT film can be removed from the solder joint region using aplasma etching technique. A metal stencil shadow mask can be used toallow the excess PAT film to be removed from the solder areas whileprotecting it in the optical area of the MOEMS cover.

The soldering process by which the frame is attached to the cover istypically done under high temperatures. This is typically not a problemfor the PAT film itself, but may be problematic for the ionizing medium.In situations where the ionizing medium cannot withstand the solderprocess temperatures, the ionizing medium can be added after the frameis soldered to the cover, for example, using a stencil printingtechnique or deposition from a liquid solution.

The overall design of the stack of materials deposited on the MOEMScover should take into consideration the characteristics of the PATfilm, such as its refractive index and thickness. PAT absorbs water, soit getters moisture from the package cavity. This can be beneficial aslong as the amount of gettered water is small (too much gettered watercan alter the optical properties of the AR coating.

Another candidate ionomer for MOEMS static dissipation films ismethacrylic acid copolymerized with ethylene, which is referred tohereinafter as MAE. MAE is an optically clear carboxylic acid basedionomer that is commercially available under the name SURLYN™. MAE iscommonly used as a transparent, heat-sealable, tough plastic film andfor sporting goods such as golf ball covers. Like PAT, MAE is notelectrically conductive until it is ionized by an ionizing medium.

Any of a variety of high molecular weight alcohols can be used as a lowvolatility ionizing medium for producing an ionized ionomer film. Forexample, a small quantity of a high molecular weight alcohol, such asglycerol, 1,2,3,4-butanetetrol, polyvinyl alcohol, or polyethyleneoxide, can be added as the ionizing medium to a PAT/alcohol solution.The solution can then deposited as a thin film onto the MOEMS cover, forexample, using the spin coating technique.

Any of a variety of ionic liquids can also be used as a non-volatileionizing medium for producing an ionized ionomer film. Ionic liquids aredescribed in (1) “Ionic Liquids May Revolutionize Chemical Processing,”www.cepmagazine.org, November 2001, pg. 16; (2) Rebecca Renner, “AnEnvironmental Solution Ionic Liquids May Replace Hazardous Solvents,”www.sciam.com, August 2001, pg. 19; (3) Joan F. Brennecke and Edward J.Maginn, “Ionic Liquids: Innovative Fluids for Chemical Processing,”AIChE Journal, Vol. 47, No. 11, November 2001, pp. 2384-2389; and (4)Juliusz Pernak and Ryszard Pozniak, “New Ionic Liquids and TheirAntielectrostatic Properties,” Ind. Eng. Chem. Res. 2001, 40, 2379-2383,which are hereby incorporated herein by reference in their entireties.Generally speaking, ionic liquids are organic salts that are liquid attemperatures under 100C., and preferably at or around room temperature.Ionic liquids have essentially no vapor pressure, so they exhibit littleor no evaporation. Many ionic liquids remain in liquid form over anextremely wide temperature range (hundreds of degrees C.). The cations,substituents, and anions of ionic liquids can be varied in almostlimitless ways to change their chemical and physical properties, andtherefore ionizing liquids can be custom made for a particular ionomermaterial (for example, to produce a ionic liquid that is soluble in theionomer) and application. The ionic liquid can be mixed with the ionomerto produce an ionized ionomer film or applied separately to the ionomerfilm to produce an ionized ionomer film. Some exemplary ionic liquidsinclude the following anions: imidazolium, quaternary ammonium,pyrrolidinium, pyridinium, and tetra alkylphosphonium. It should benoted that, while many ionic liquids exhibit electrostatic properties,an embodiment of the present invention uses the ionic liquid not for itsionic or electrostatic properties per se, but rather as an ionizingmedium for producing an ionized ionomer film.

A technique for depositing a PAT film from solution using a spin coatingtechnique is described above. It should be noted, however, then PAT andother ionomer films are not required to be deposited from solution.Other techniques can be used to deposit ionomer films. Some exemplarytechniques for depositing ionomer films are described in C. J. Brumliket al., “Plasma polymerization of sulfonated fluorochlorocarbon ionomerfilms,” J. Electrochemical Soc., 141(9), 1994, pp. 2273-2279, which ishereby incorporated herein by reference in its entirety.

Teflon AF Films

Teflon AF is a hard, crystal clear thermoplastic that is stable atelevated temperatures. It has a relatively low refractive index of 1.29to 1.31. Like other types of Teflon, it is chemically inert andoptically stable. Unlike other Teflons, however, it is soluble incertain fluorocarbon solvents, so it can be deposited as a thin film onglass.

The use of Teflon AF as a single layer anti-reflective coating isdescribed in N. Bazin et al., “Formation of Teflon AF Polymer Thin Filmsas Optical Coatings in the High Peak Power Laser Field,” SPIE Proc.,3492, 1999, pp. 964-969, which is hereby incorporated herein byreference in its entirety, and in two earlier reports cited therein.Generally speaking, the wavelengths used in optical switchingapplications are different from those examined in this report, but theoptical principles are essentially the same. Use of Teflon AF as ananti-reflective coating on MOEMS covers has several attractions. TeflonAF can be spin coated, which is less expensive than certain multilayervacuum deposition techniques, and other deposition techniques can alsobe used. With Teflon AF, re-work is not a problem. Teflon AF has lowinventory costs, as low value glass blanks can be inventoried and coatedas needed. Finally, Teflon AF is easier to test than standard multilayeranti-reflective films that may produce ghost images at visiblewavelengths (630 nm is often used in MOEMS testing).

In order to achieve anti-reflective characteristics, the refractiveindex of glass, air, and the Teflon AF coating should be related asfollows:n _(Glass)=(n _(Air) n _(Teflon))^(1/2)

With n_(Teflon)=1.3 and n_(Air)=1.0, an ideal glass would have arefractive index of 1.69.

Furthermore, the thickness of the anti-reflective film should be an oddmultiple of one fourth of the optical wavelength in the film (i.e., λ/4,3λ/4, 5λ/4, etc.). For λ=1.5μ, the thickness t of the anti-reflectivefilm should be:t≈1.5*m/(4*1.3)

where m is an odd integer. Thus, the thickness t of the anti-reflectivefilm could be approximately 0.3μ or 0.9μ or 1.44μ or 2.0μ for values ofm of 1, 3, 5, and 7, respectively.

Reflection is reinforced when m is an even integer (i.e., λ/2, λ, 3λ/2,etc.). Therefore, to achieve anti-reflective performance, thicknessshould be carefully controlled. For example, thickness could be in arange approximately 0.2-0.4μ or 0.8-1.0μ or 1.34-1.54μ or 1.9-2.1μ forvalues of m of 1, 3, 5, and 7, respectively.

Pure Teflon AF is not electrically conductive and therefore does notwork for static dissipation of MOEMS covers.

In one embodiment of the present invention, Teflon AF is replaced by anionomer film that is made to be electrically conductive as describedabove. Such a film also reduces surface reflections when its thicknessis controlled as described above for Teflon AF.

In another embodiment of the present invention, conductive particles areadded to the Teflon AF in sufficient quantity to make the resulting filmelectrically conductive while maintaining sufficient opticaltransparency. Percolation theory is a statistical method for calculatingthe minimum volume percentage of conductive particles that must bedispersed in a dielectric medium in order to achieve electricalcontinuity across that medium. Percolation theory is often applied inthree dimension, although it is used in this application more for atwo-dimensional application. Use of high aspect ratio particlessubstantially reduces this percentage. Therefore, in an embodiment ofthe present invention, single wall carbon nanotubes (SWNT) are used toform a conductive percolation network when dispersed in the thin TeflonAF coating. SWNT particles are good candidates for forming a conductivepercolation network in a Teflon AF film because they are electricallyconductive, have a high aspect ratio (i.e., a length-to-diameter ratioon the order of 10,000) in order to reduce the volume percentagerequired for electrical continuity across the film, and aresubstantially thinner (approximately 2-10 nm in diameter) than theoptical wavelength and so should be substantially invisible when alignedin a plane perpendicular to the optical axis. High aspect ratioparticles in spin cast solutions are generally “in-plane,” and, even ifthis criterion is not fully met, the nanotubes only occlude a smallfraction of the optical window area because the volume percentage is lowdue to the high aspect ratio.

In order for the Teflon AF film with SWNT particles to operatesufficiently, the SWNT particles should be dispersed throughout theTeflon AF material in a substantially uniform fashion without clumps.This dispersion can be accomplished in any of a number of ways,including dispersing the SWNT particles in a fluorocarbon solvent beforeor after adding the Teflon AF. Dispersion can be induced usingultrasound, high shear mixing, freeze-thaw cycling, low frequencyelectric fields, or other methods. Once dispersed, particle settling isunlikely because the specific gravity of the nanotubes is similar toboth Teflon AF and fluorocarbon solvents.

It should be noted that applying an antistatic film layer over an ARcoating can substantially affect AR performance. Therefore, the designof the AR film stack should account for the optical properties of theantistatic film layer.

Some antistatic films can act as single-layer AR films. For example,Teflon AF and certain Nafion-based films can function as single-layer ARfilms. Among other things, single-layer AR films are less costly thanmultiple-layer AR films. However, single-layer AR films typicallyprovide effective AR performance only over a narrow wavelength range.

Another embodiment of the present invention uses surface forces to holdconductive particles, such as SWNT, in a conductive percolation networkon cover surfaces. Since this embodiment does not insert a film into theoptical path, AR film stacks made from standard materials that are notelectrically conductive can be used without modification (the conductiveparticle network on the surface of the package window drains electricalcharges before the accumulate to harmful levels). Maintaining a stablenetwork without a film matrix is possible because of the surfaceadhesion forces that arise when two objects touch. These surface forcesinclude capillary, electrostatic, van der Waals forces, and severalchemical forces. Some of these forces are observable in everyday life.Others, such as van der Waals forces, are less widely recognized. Vander Waals forces arise from transient dipole moment interactions ofatoms.

Surface forces become increasingly dominant as particle size is reduced.This occurs because small particles have very little mass. They areessentially all surface. Surface-to-mass ratio is further increased inhigh aspect ratio particles. As a result, surface forces make it verydifficult to remove small diameter, high aspect ratio particles from asurface. This characteristic is particularly applicable to thisembodiment of the present invention because the application requiressmall particles to avoid optical interaction, and electrical percolationperformance is enhanced when the conductive particles have a high aspectratio. Once the particles are deposited, their small size ensures thatsurface forces will securely bind them to the surface.

There are several techniques that can be used to manufacture particlenetworks that are stabilized by surface forces. In general, theparticles are dispersed in a carrier medium. This dispersion is thenapplied to the cover glass surface where the carrier medium is removed.For example, when a volatile liquid is used as the carrier medium, a dipcoating or spin coating process will leave the particles on the coverglass surface as a residue network that is bound by surface forces afterthe liquid is volatilized. This is only an illustrative example. Thecarrier medium can be solid, liquid, gas, or plasma. Removal can be bysublimation, volatilization, or exposure to reduced pressure. Fluidmedia can be at, above, or below supercritical conditions. A keycriterion is that the particles must be substantially dispersed in themedium prior to deposition on the surface.

Another embodiment of the present invention uses surface forces to holdconductive fluids, such as ionic liquids, as a conductive film that isonly a few monolayers thick on cover surfaces. In this thickness range,optical effects are insignificant and the slightly conductive film willdrain electrical charges from the surface of the package window beforethey accumulate to harmful levels.

The present invention may be embodied in other specific forms withoutdeparting from the true scope of the invention. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive.

1. An apparatus comprising: a substrate having a micromachined opticaldevice disposed thereon; a cover coupled to the substrate so as to coverthe optical device; and an optically transparent conductive coatingdisposed directly or indirectly on an inside surface of the cover facingtoward the micromachined optical device, wherein an electricalconnection is made to the optically transparent conductive coating forstatic dissipation.
 2. An apparatus according to claim 1, wherein theoptically transparent conductive coating comprises an ionomer that is atleast partially ionized.
 3. An apparatus according to claim 2, whereinthe ionomer comprises one of: a sulfonic acid based ionomer such asperfluorosulfonic acid copolymerized with tetrafluoroethylene; and acarboxylic acid based ionomer such as methacrylic acid copolymerizedwith ethylene.
 4. An apparatus according to claim 2, wherein theoptically transparent conductive coating further comprises an ionizingmedium for ionizing the ionomer.
 5. An apparatus according to claim 4,wherein the ionizing medium comprises one of: water; an alcohol such asglycerol, 1,2,3,4-butanetetrol, polyvinyl alcohol, or polyethyleneoxide; and an ionic liquid.
 6. An apparatus according to claim 1,wherein the optically transparent conductive coating comprises a TeflonAF film having dispersed therein a sufficient quantity of electricallyconductive particles for making the Teflon AF film electricallyconductive while maintaining sufficient optical transparency.
 7. Anapparatus according to claim 6, wherein the electrically conductiveparticles comprise single wall carbon nanotubes.
 8. An apparatusaccording to claim 7, wherein the single wall carbon nanotubes aredispersed throughout the Teflon AF film in a sufficient volumepercentage to provide electrical continuity across the film.
 9. Anapparatus according to claim 7, wherein the single wall carbon nanotubesare substantially aligned in a plane perpendicular to an optical axis soas to maintain sufficient optical transparency.
 10. An apparatusaccording to claim 1, wherein the optically transparent conductivecoating comprises conductive particles held in a percolation networkthrough surface forces without the use of a matrix film.
 11. Anapparatus according to claim 1, wherein the optically transparentconductive coating comprises an ionically conductive fluid applied at athickness that is optically insignificant.
 12. An apparatus according toclaim 11, wherein the ionically conductive fluid comprises an ionicliquid.
 13. An apparatus according to claim 1, wherein the opticallytransparent conductive coating is at least partially organic.
 14. Anapparatus according to claim 1, wherein the optically transparentconductive coating is deposited on the cover material in a mannersufficient to provide anti-reflection in addition to static dissipation.15. An apparatus according to claim 14, wherein the opticallytransparent conductive coating for anti-reflection and staticdissipation is deposited to a thickness substantially equal to an oddmultiple of one fourth of a predetermined optical wavelength in thefilm.
 16. An apparatus according to claim 1, further comprising: anoptically transparent conductive coating disposed directly or indirectlyon an outside surface of the cover facing away from the micromachinedoptical device.
 17. An apparatus according to claim 1, wherein thesubstrate includes a cavity and the micromachined optical deviceincludes a mirror structure bonded to the substrate within the cavity,and wherein the cover material with optically transparent conductivecoating is coupled to the substrate across the cavity.
 18. An apparatusaccording to claim 1, wherein the cover material comprises a metallizedfilm for bonding to a metal frame, and wherein the optically transparentconductive coating contacts at least a portion of the metallized film.19. An apparatus according to claim 18, further comprising the metalframe bonded to the metallized film.
 20. An apparatus according to claim1, wherein the optical device comprises integrated electronic circuitry.